This invention relates to the art of laying pipe, particularly water mains.
Municipal water mains are made of various materials. Smaller mains, under about twelve inches in diameter, are made of plastic, usually PVC, while larger mains are made of ductile iron. Both types of pipe are generally formed with a male portion at one end of each pipe segment which fits into the free female end of the adjoining pipe and seals to it. Generally, the female end is formed as a bell of greater outside diameter than the length of the pipe.
Presently, water mains are laid by digging a trench of the appropriate depth, typically several feet, and width, typically only a few inches wider than the pipe diameter, usually by means of a power trencher, excavator or backhoe. The pipe is then laid with the aid of a crane or other grappling device and a worker in the trench who guides the pipe into position and moves it forward axially into engagement with the female end of the previously laid pipe segment.
It has long been recognized that this process is tedious, time-consuming, and expensive. To solve these problems, several proposals have been made for pipe-handling attachments for power equipment. These attachments are intended to allow the operator of the equipment to handle pipe segments without aid. For example, Hilfiker, U.S. Pat. No. 3,834,566, uses a shaft attached to the rear of a bucket of a conventional backhoe excavator. The shaft is inserted into the end of a pipe section and supports the pipe as it is lowered into the trench. This approach is simple, but it does not provide any positive connection to the pipe, so that the beam must be tilted slightly upward to prevent the pipe from slipping off it. This is a problem in itself, and it has the consequence that the forward, male end of the pipe section, which must be mated to the previously-laid pipe line, is higher than the other end of the section. Therefore, mating the sections is difficult. The system is likewise liable to scratch iron pipe or break plastic pipe.
A more recent example of such an attachment is Recker, U.S. Pat. No. 5,219,265. In this patent, a grapple assembly is attached to the stick or crowd arm of a tracked hydraulic excavator. The grapple provides a more positive grip on the pipe, and the device permits the pipe segment to be angled downwardly as it is placed in the trench. It depends, however, on eccentric mounting of both the pivot which attaches it to the excavator and the pair of tongs which grip the pipe segment, and therefore makes handling and orienting pipe segments more difficult. It is apt to scratch iron pipe and damage plastic pipe. It also appears to require a trench much wider than the outer diameter of the pipe, and thus requires a great deal of extra earth removal.